This invention relates to digital data transmission and more particularly to an apparatus and method for selecting from multiple data streams to produce a single data output.
Various types of information may be converted to a digital format and the digital data then transmitted to a user location as a radio frequency signal comprising a digital data stream. A single user location may be able to receive these digital radio frequency transmissions from multiple sources. For example, a user may receive signals directed from one or more terrestrial transmitters. Also, the same user may be able to receive digital radio frequency signals from one or more satellites. Regardless of the source of the radio frequency signals which comprise the digital data stream, each data stream must be processed at the user location to provide useful information.
Direct broadcast satellite (DBS) television transmission is one example of digital radio frequency transmission. In DBS transmission, digital signals on a number of different carrier frequencies are transmitted from a satellite and these multiple carrier frequencies together comprise a data stream. The frequency spectrum now allotted to DBS transmissions comprises the spectrum from 12.2 to 12.7 GHz. Each carrier frequency carries data for several different discrete outputs, which in the DBS example, comprise television channels. In order to use the DBS data stream, the entire data stream is picked up by a suitable antenna and the frequencies are down converted to an intermediate frequency below the radio frequency level. A receiver at the user location demodulates the desired carrier frequency and decodes the demodulated signals to produce a desired output comprising a channel input for a television set.
It is an object of the invention to provide an apparatus and method for selecting from multiple data streams transmitted on one or more common frequencies and processing the selected data stream.
In order to accomplish this object, an apparatus according to the invention includes a plurality of signal input paths to a single receiver/signal processor. A switching arrangement associated with the signal input paths enables only one of the paths at a given time for communicating a data stream to the receiver/signal processor. Each signal input path may receive a separate data stream including signals at one or more frequencies which may or may not be common to frequencies for signals received on another one of the input paths. By enabling only one input path at a time, the switching arrangement prevents common frequency signals from interfering with each other. Furthermore all of the signals from each source may be processed by the single receiver/signal processor, thus avoiding duplicate signal processing equipment at the user location.
As used in this disclosure, the term xe2x80x9cdata streamxe2x80x9d means digital data transmissions on one or more frequencies from a single source. The frequency or frequencies may be any frequency including radio frequencies and lower frequencies. For example, a data stream may comprise signals transmitted at radio frequencies from a satellite and may also comprise the same signals after down conversion to intermediate frequencies. Also, as used herein xe2x80x9cdataxe2x80x9d shall mean any digital data and shall not be limited to data producing any particular type of output. For example, xe2x80x9cdataxe2x80x9d may comprise the digital signals required to produce a television input for a standard television set. As another example, xe2x80x9cdataxe2x80x9d may comprise digital signals representing Internet communications. As yet another example, xe2x80x9cdataxe2x80x9d may comprise digital voice or telephone information.
The switching arrangement includes a suitable switching device connected in each input path. Each switching device is enabled for passing the data stream only in response to an enable signal supplied to the respective switching device. In the absence of an enable signal the respective switching device serves to block the data stream on the particular input path. The plurality of the input paths meet at a junction having a single output which is connected to the input of the receiver/signal processor. The receiver/signal processor receives signals from the single enabled input path and processes the signals in a manner well known in the art to produce a desired data output.
The apparatus according to the invention has associated with it a separate radio frequency receiving arrangement for each signal input path. Each radio frequency receiving arrangement includes a suitable antenna for receiving signals from a single transmission source. Each radio frequency receiving arrangement further includes a suitable down converter for converting the radio frequency signals to intermediate frequency signals. Each separate data stream of intermediate frequency signals is applied to a different one of the signal input paths to the processing apparatus according to the invention.
In the preferred form of the invention, the processing apparatus includes a controller for controlling the switching arrangement and the various components of the receiver/signal processor. The controller responds to a user entered select input which is associated with certain data within one of the input data streams which may be processed to produce a desired data output. In response to a select input, the controller retrieves from a memory device signal input information for controlling the switching arrangement and signal processing information for controlling the receiver/signal processor. The controller uses the signal input information to enable the signal input path which carries the data stream containing the data for the selected output. The signal processing information causes the receiver/signal processor to tune to the correct carrier frequency carrying the desired data, demodulate transmitted signals, and finally decode the demodulated signals to produce the desired data output.
These and other objects, advantages, and features of the invention will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawing.